1. Technical Field
The present invention relates to a light-emitting element head in which plural light-emitting element chips are arrayed, image forming apparatus including a light-emitting element head in which plural light-emitting element chips are arrayed, and a signal supply method.
2. Related Art
In an electrophotographic image forming apparatus such as a printer, a copy machine or a facsimile machine, an image is formed on a recording paper sheet as follows. Firstly, an electrostatic latent image is formed on a charged photoconductor by causing an optical recording unit to emit light on the basis of image information. Then, the electrostatic latent image is made visible by being developed with toner. Lastly, the toner image is transferred on and fixed to the recording paper sheet. As such an optical recording unit, in addition to an optical-scanning recording unit that performs exposure by laser scanning in a first scan direction using a laser beam, an optical recording unit using the following light-emitting element head has been employed in recent years. This light-emitting element head includes a large number of light-emitting element chips arrayed in a first scan direction, and each light-emitting element chip includes a light-emitting element array formed of light-emitting elements such as light emitting diodes (LEDs) arrayed in a line.
Such a light-emitting element head including a large number of light-emitting element chips arrayed thereon requires as many lighting signals as correspond to the number of light-emitting element chips. Accordingly, in the light-emitting element head, the number of lighting signal bus lines increases as the number of light-emitting element chips increases. In addition, the number of current buffer circuits each having a large current drive capability also increases with increase in the number of light-emitting element chips since the lighting signals supply a current to the light-emitting elements.
Hence, a light-emitting element head including a large number of light-emitting element chips has the following problems: the size of a drive IC of the light-emitting element head increases as the number of light-emitting element chips increases in the light-emitting element head; and the printed circuit board of the light-emitting element head needs to have a larger width in order to allow a large number of low-resistance lighting signal bus lines to be arranged thereon. The width of the printed circuit board may be reduced by employing a multi-layer printed circuit board, which however causes increase in cost.